1. Field of the Invention
The present invention relates to a vehicle having driven and driving wheels to which tires are attached, and more particularly to a vehicle having a tire wear evaluation system which evaluates wear of tires using wheel speeds of driven and driving wheels.
2. Description of the Related Art
In open-pit mines or similar sites, such vehicles as dump trucks repeat a transportation cycle that they carry soil accumulated by a shovel to a given place and dump it there, and return to the original place in order to load soil again.
For higher efficiency in mine operation, there has been an increasing tendency toward larger dump trucks and very large load capacities. There are even large vehicles which weigh approximately 190 tons and have a load capacity of approximately 360 tons.
Such dump trucks are often used on a basis of three shifts per day and some of them are operated 20-24 hours a day, so their operation rates are very high. Therefore, their tires wear more quickly than the tires of ordinary passenger vehicles.
Generally, as tires wear, they are more likely to slip during acceleration and lock up during deceleration and it may become difficult to maintain the running stability of the vehicles. In addition, many mines have strict safety rules including a rule which prohibits dump trucks from being driven in a rainy weather in which tires easily slip or lock up.
Therefore, for the purpose of assuring running stability of dump trucks, it is very important to check the tires for wear.
With this background, JP-A No. 2006-162384 describes a method for detecting tire wear automatically. The method described there detects tire wear in which the outer circumference and outer diameter of a tire are calculated from the travel distance in a given period as determined from the position of the vehicle detected by GPS and the wheel revolution speed (number of revolutions) in that period and compared with the outer circumference and outer diameter of the same tire at an earlier time when it was not worn.